Ultrasonic cutting blade with cooling

ABSTRACT

An ultrasonic surgical blade has a blade body with a smooth continuous cutting edge and a shank connected at one end to the blade body and operatively connectable at an opposite end to a source of ultrasonic vibrations. The shank is provided with an axially extending bore for the conveyance of cooling fluid to the cutting edge, while the blade body is provided with an axially extending through-slot communicating at one end with the bore. The blade body is preferably provided at an end opposite the shank with a recess communicating, with the bore for distributing fluid from the slot towards the cutting edge. The recess preferably has a configuration which parallels at least a portion of the cutting edge. Where the cutting edge is circular and the blade body has a planar surface between the fluid distribution guide surface and the cutting edge, for instance, the recess has a fluid distribution surface inclined with respect to the planar blade surface and extending along a circular arc.

FIELD OF THE INVENTION

This invention relates to an ultrasonic cutting blade. The blade isparticularly useful in a surgical application to cut tissue such ascartilage and bone.

BACKGROUND OF THE INVENTION

In the field of orthopedics, the cutting of living bone is aprerequisite for many procedures. Such procedures include thereconstruction of damaged tissue structures due to accidents, thegrafting of healthy bone into areas damaged by disease, or thecorrection of congenital facial abnormalities like a receding chin line.Over several centuries, these tasks were performed through theutilization of devices called bone saws.

Traditional bone saws are categorized into several basic categories.Hand powered saws or drills are just that, hand held devices whichrequire the operator to move the device in a fashion similar to thatused for carpentry tools. Powered devices, whether electric orpneumatic, are of either the reciprocating or rotary type. Thereciprocating devices use a flat, sword like blade where the back andforth motion is provided by a motor instead of the hand. The rotarydevices use a rotating motor to spin a drill bit or a blade which hasteeth arranged around its circumference similar to a table saw blade.All of these traditional bone saws are used today in medical proceduresaround the world.

While traditional saws are functional, they have many disadvantages.With either the band or reciprocating saws, for instance, it is not easyto initiate and direct a cut. A cut must start from an edge or,alternatively, a starting hole must be used. To create a starting hole,a drill or similar instrument is operated to bore into the bone.Subsequently, a cutting blade is inserted into the bored hole. The usercan then proceed to cut. Alternatively, a rotary type blade may be used.However, when a rotary blade is used, the cut must follow a relativelystraight path to prevent the blade from binding in the cut. With allblades the ability to create a curved or compound angle cut is extremelylimited by the blade chosen. The relatively thick blades have a widekerf; so that a significant thickness of the viable bone is lost in thecutting procedure. Physicians would like this width to be as thin aspossible in most procedures where reconstruction is necessary.

Above all, the relatively slow linear or tangential speeds ofconventional bone saw blades coupled with the teeth necessary forcutting result in high frictional losses, which becomes manifested asheat. Heat will cause necrosis of the tissue if the bone temperaturesreach 47° C. for more than a few seconds. When tissue necroses, the bonerecedes after the surgery as the necrotic bone is overgrown. During suchnatural post-surgical tissue developments, the thickness of the cuts inthe bone actually increases. The bone rescission process must becomplete before healing can begin. To prevent the shortening of thelength of the bone, metal plates and screws are used to fix the bonefragments in proper position. All of these factors obviously lead toincreased operative time, and more importantly, to dramaticallyincreased healing time, since the bone must knit across a greater span.Some studies have shown the strength of the bone to be effectednegatively as well.

When an upper or lower jaw is to be cut in elective surgery, the heatingeffect of traditional saws requires even more extraordinary interventionto prevent damage. Cutting the jaw between the teeth will cause loss ofteeth if the bone is damaged or does not heal quickly. To prevent thetooth loss, the teeth must be spread apart preoperatively; sometimesforcing the patient to wear braces for up to 6 months before theoperation can take place. In these cases, the costs and patientdiscomfort increases dramatically.

To limit the tissue temperature rise in an attempt to reduce necrosis,some traditional surgical saws provide cooling liquid to the surgicalsite. See, for instance, U.S. Pat. No. 4,008,720 to Brinckmann et al.These devices typically introduce coolant into spaces between segmentson the cutting edge or rely on spray methods to flood the cutting sitewith fluid. Another technique employed by clinicians is to make verylight cuts and increase the time between passes of the tool. Coupledwith irrigation of the area, bone temperature rise is reducedmeasurably. Of course, this technique increases operative time andclinician fatigue.

Several researchers have proposed the use of ultrasonic tools for boneseparation. The use of ultrasonic surgical instruments for cuttingthrough various tissues is well known. While these devices are superiorto the traditional saws in several aspects such as reduced kerf size,reduced noise, and superior ability for making complex geometric cuts,the temperature rise in bone due to frictional heating at theblade/tissue interface is still a significant problem. The problem isexacerbated with the use of ultrasonics due to the rapid motion involvedas compared to that of traditional reciprocating saws. Some designershave tried to reduce heating by modifying the cross-section of thecutting blade. U.S. Pat. No. 5,188,102 to Idernoto, U.S. Pat. No.4,188,952 to Loschilov, and U.S. Pat. No. 5,261,922 to Hood all showdesigns for cutting which have modified cross sections to reducefrictional heating.

Several ultrasonic devices have provided cooling to the cutting bladewith varied degrees of success. U.S. Pat. No. 4,823,790 to Alperovich etal. shows a design for a cryogenically cooled scalpel blade. However,this design may actually damage viable tissue by freezing. In addition,this design does not provide any coolant to surrounding tissue not indirect contact with the blade.

U.S. Pat. Nos. 5,205,817, 5,188,102, and 4,832,683 all to Idemoto showexamples of ultrasonic instruments with provisions for fluid cooling.These instruments, however, either do not provide optimal coolant flowwhere it is needed, mainly at the cutting portion of the blade, or forones that do provide coolant at the tip, they interrupt the cutting edgewith holes for the coolant. An interrupted, uneven cutting edge hindersmanipulation and makes it difficult to guide the blade on the bonesurface.

One phenomenon associated with ultrasonic tooling which acts to hinderthe beneficial effects of irrigating the operative site is ultrasonicatomization. When an ultrasonically vibrating body is brought intocontact with fluid, that fluid is broken into small droplets which havea size inversely proportional to the frequency of vibration. In otherwords, the higher the frequency, the smaller and more mobile the liquiddrop. Droplets created by ultrasonic vibrations can be very small insize, with some being less than 1 micron in diameter. This phenomenon iswell known to the art. In fact, many devices intended to atomize liquid,such as room humidifiers, medical nebulizers, and industrial spraynozzle are based upon this principle. In the operating theater, however,the presence of nebulized particles is not appreciated, since theseparticles may contain viral or bacterial agents. Also, some of the fluidwill be atomized before reaching the operative site, reducing thecooling efficiency. An effective way to insure the liquid transport isneeded.

SUMMARY OF THE INVENTION

The present invention recognizes the need which exists for an improvedblade for use with ultrasonic cutting instruments. The invention isdirected to an ultrasonic cutting blade which allows thin kerf cuts,does not require predrilled holes for cutting, allows complex geometriccuts, has a continuous cutting surface, and provides for liquidirrigation at primarily the blade/tissue interface. More specifically,the present invention pertains to an ultrasonically vibrated cuttingblade with a provision for delivery of a cooling medium for reducing andlimiting thermal damage to living tissue. The present inventionspecifically targets the application of cutting viable bones in surgery,although the device is not exclusive to this application.

An ultrasonic surgical blade in accordance with the present inventioncomprises a blade body having a smoothly continuous cutting edge andfurther comprises a shank connected at one end to the blade body andoperatively connectable at an opposite end to a source of ultrasonicvibrations.

Preferably, the cutting edge is disposed in a single plane and has anarcuate section. The arcuate section is substantially circular and isdisposed on the blade body opposite the shank. The cutting edgeadditionally includes a pair of straight sections continuous with thecircular section at opposite ends thereof. Where the blade body has alongitudinal axis, the straight sections are oriented substantiallyparallel to the axis.

In accordance with another feature of the present invention, the shankis provided with an axially extending bore for the conveyance of coolingfluid to the cutting edge, while the blade body is provided with anaxially extending through-slot communicating at one end with the bore.The blade body is preferably provided at an end opposite the shank witha recess communicating with the bore for distributing fluid from theslot towards the cutting edge. The recess preferably has a configurationwhich parallels at least a portion of the cutting edge. Where thecutting edge is circular and the blade body has a planar surface betweenthe fluid distribution guide surface and the cutting edge, for instance,the recess has a fluid distribution surface inclined with respect to theplanar blade surface and extending along a circular arc.

Where the fluid distribution guide surface is an inclined surfaceextending between the passageway or bore and the cutting edge.

The basic advantages derived from the present invention are as follows.The blade edge is continuous, i.e., having no teeth, serrations orvoids. This continuity provides a smooth contact surface essential whenmaking precise cuts. In contrast, in an ultrasonic cutting blade havingteeth, serrations or interruptions, the feel of the instrument changesand the instrument is more difficult to guide as the teeth, serrations,or interruptions are moved across the bone at the surgical site. Teethon the blade edge not only do not improve the cutting speed but make itdifficult to keep the edge on a predetermined cut line. The continuousblade edge of the present invention also gives the cutting process aconsistent feel to the surgeon, similar to the feel of a standardscalpel blade.

Another advantage of the present ultrasonic instrument is the structurewithin the blade for providing irrigation to the blade edge.Experimentation has shown that atomization is substantially reduced.Additionally the coolant fluid is delivered along the side of the bladeand into the cut, but the delivery mechanism does not interrupt thecutting edge as has been found to be significant in the instrument'sfeel and performance.

The advantages to this invention beyond its use are in its predictedresults there will be less dead bone and a small cut width. This keepsthe cut narrow and provides for quicker healing than if the bone wereoverheated to necrosis or if the cut was wider.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall view of a surgical system having an ultrasoniccutting blade in accordance with the present invention.

FIG. 2 is a perspective view of an ultrasonic probe and an associatedultrasonic blade in accordance with the invention.

FIG. 3 is a perspective view, on an enlarged scale, showing the blade ofFIG. 2 and a blade shank.

FIG. 4 is a side elevational view of the probe and blade of FIG. 2.

FIG. 5 is a longitudinal or axial cross-sectional, view taken along lineV—V in FIG. 4.

FIG. 6 is side elevational view of the cutting blade of FIGS. 2-5.

FIG. 7 is a top plan view of the cutting blade of FIGS. 2-6.

FIG. 8 is a front elevational view of the cutting blade of FIGS. 2-7.

FIG. 9 is a cross-sectional view taken along line IX—IX in FIG. 7.

FIG. 10 is a longitudinal cross-sectional view of a portion of the probeand the blade of FIGS. 2, 4, and 5, with arrows indicating a flow pathof irrigant.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, an ultrasonic surgical system includes a handpiece10 carrying a cutting blade 12. Handpiece 10 is attached to blade 12 viaa probe 14 and further includes a housing 16 which encases apiezoelectric crystal assembly of the kind disclosed in U.S. Pat. No.5,371,429 to Manna. In response to a sinusoidal oscillating signaltransmitted over a cable 18 from an ultrasonic generator 20, the crystalassembly in the probe produces longitudinal ultrasonic pressure wavestransmitted through probe 14 to blade 12. Signal generator 20 isactivated via a footswitch 22. Handpiece 10 is also connected to anirrigation pump 24 via a tube 26. Pump 24 moves an irrigant liquid froma reservoir or IV type hanging bag 28 through tube 26 to handpiece 10 inresponse to a signal carried over a cable 30 from signal generator 20under the control of footswitch 22.

The mechanical vibration produced by the piezoelectric crystal assemblyin handpiece 10 is amplified mechanically via the transducer shape andstill further by the shape of probe 14 and blade 12, using techniquesknown to those skilled in the art of ultrasonics. Probe 14 is attachedto handpiece 10 via an externally threaded connection 31, shown in FIG.2. Probe 14 is thus replaceable by the user to facilitate the use ofdisposable sterile blades 12 from one procedure to the next. Handpiece10 may be sterilized by autoclaving as well as by other conventionalmethods. While probe 14 can be sterilized, maintaining a good cuttingedge and cleanliness is such a key issue that a disposable tip or adisposable probe/tip assembly is envisioned. The primary purpose ofprobe 14 is to mechanically amplify the vibration from the piezoelectrictransducer assembly and transmit that vibration through to cutting blade12.

As illustrated in FIG. 3, cutting blade 12 includes an integral shankportion 32 having an external screw thread 34 for replaceably mountingthe blade to probe 14. Alternatively, blade 12 may be permanentlyattached to probe 14. In the former case, blade 12 is tightened by awrench (not shown) applied to wrench flats 36 on shank portion 32. Blade12 is shaped to amplify the longitudinal vibratory motion. Morespecifically, blade 12 includes a tapered or wedge-shaped portion 38connected to shank portion 32 for focusing or concentrating ultrasonicvibratory energy and transmitting the energy to a planar portion 40 ofblade 12. The whole transducer, horn and tip assembly is designed toresonate in a longitudinal or back and forth type of motion. This motionprovides the cutting action at the tip of blade 12.

Planar blade portion 40 is provided at an end opposite tapered portion38 and shank 32 with a blade edge 42 including a central circularlyarcuate section 44 and a pair of linear end sections 46 and 48. Blade orcutting edge 44 is sharpened along a full radius of arcuate section 44,as well as along straight sections 46 and 48, with a knife type edgethat can smoothly be drawn back and forth in a brushing type motion.This cutting edge structure allows the user to maintain a constantmotion at the tip, which has been shown to be important to preventoverheating of the tissue at the surgical site.

As further illustrated in FIGS. 3, 5, 7, 9, and 10, blade 12 alsoincorporates structure providing a path for coolant from irrigation pump24 (FIG. 1) to reach blade edge 42, as well as tissues being cut duringa surgical procedure. For conducting irrigant to blade edge 42 and thesurgical site, probe 14 is formed with an axial passageway or bore 50(FIGS. 5 and 10) which communicates with an axial passageway or bore 52in blade 12 and more particularly in shank 32 and part of tapered bladeportion 38. The irrigation fluid is typically a sterile saline solutionsupplied in hanging bag 28 (FIG. 1). Bag 28 is punctured with a ventedIV spike supplied at the end of a sterile tube set 54. The spike allowsthe fluid to flow into a silicone tube section 55 of tube 26 of set 54.Silicone tube section 55 passes through pump 24 which takes the form ofa peristaltic or roller type pump. Pump 24 pushes the fluid along tube26 to a connection at the handpiece 10. The fluid travels through anintegral channel inside the handpiece 10, as described in U.S. Pat. No.5,371,429. From handpiece 10 the fluid travels through probe 14 to blade12.

Passageway or bore 52 terminates in an open longitudinal channel or slot56 that enables the coolant to spread out and onto the planar portion 40of blade 12. This open channel or slot 56 is an important feature whenblade 12 is located deep in a cut because the channel or slotdistributes irrigant all along the sides or lateral surfaces of planarblade portion 40 and not in only specific locations, as indicated byarrows 60 in FIG. 10. At an end of channel or slot 56 oppositepassageway or bore 52 is disposed a recess 58 in planar blade portion40, as shown in FIGS. 2, 3, and 7. Recess 58 has an arcuate or, morespecifically, circular, configuration (see FIG. 7) optionally concentricwith that of arcuate blade edge section 44. Recess 58 is defined in partby a pair of inclined surfaces 61 and 62 (FIG. 9) for distributingirrigant from channel or slot 56 towards blade 40 and then to circularcentral blade section 44, along the length thereof. The fluid travelingdown channel or slot 56 will encounter inclined surfaces 60 and 62 ofrecess 58 which exhibit an incident angle that deflects the fluid intothe cut (FIG. 10) while minimizing splash back.

The resonant portions of the transducer and probe 14 are typically madeof a low acoustic loss material that should also be biocompatible.Titanium 6A14V alloy is the preferred choice but other alloys may beacceptable. Blade 12 is constructed of Stainless Steel 17-4PH alloy.This material has a lower acoustic loss when compared to other stainlesssteels yet is robust enough to machine and hold an edge with therequired geometry versus the titanium alloy used elsewhere. If blade 12and horn or probe 14 are made in one continuous piece the stainlesssteel alloy may be used.

To operate the system of FIG. 1, blade edge 42 is brought into contactwith the intended surgical site. The system is activated via footswitch22, the pressing of which causes ultrasonic generator 20 and irrigationpump 24 to operate. The ultrasonic signal from the generator 20 istransformed via the piezoelectric transducer crystals (not shown) inhandpiece 10 into a mechanical vibration. This vibration is amplifiedand coupled from the transducer assembly to probe 14 and to blade 12.The vibrations at blade edge 42 perform the cutting and separation ofbone tissue at the surgical site.

Blade edge 42 is moved back and forth in a brushing type of movement tokeep the tip in motion. This cutting technique reduces the dwell time inany given location, which aids in minimizing any temperature rise at thesurgical site. A continuous moving of the blade tip or edge 42 alsoprevents the blade from blocking the conveyance of irrigant fluid to anygiven spot and allows the irrigation fluid an opportunity to flow tothat area. The smooth continuous blade edges 44, 46, 48 make it easierfor the user to keep the blade 12 in motion and to keep it on apreselected cut line or track at the surgical site. Serrations, teeth,protrusions or indentations which are generally provided on otherultrasonic surgical blades hinder this mode of operation since theirregular surface causes the blade to drag and impedes the guiding ofthe blade. The ultrasonic vibrations also facilitate movement of blade12 on the tissue surfaces at the surgical site since the vibrating bladebreaks contact with the tissue on each vibratory cycle.

When the edge 42 of blade 12 begins to penetrate below the surface ofthe tissue, channel or slot 56 becomes particularly beneficial. Duringthe initial phase of a surgical cutting procedure, channel or slot 56only guides the fluid toward cutting edge 42. Subsequently, where bladeedge 42 but not recess 58 is below the tissue surface, the recess designallows the irrigation fluid to flow down to the tip of blade 12 andhelps to distribute the fluid across or along the blade edge. During afurther stage of a surgical cutting operation, when recess 58 is locatedbelow the outer tissue surface, channel or slot 56 allows the irrigationfluid to flow out on both sides or lateral surfaces (not separatelydesignated) of blade 12 and along the full length of the blade. Thisprocess provides cooling irrigation and lubrication to reduce thefrictional heating on the sides of the blade.

The pressure on blade 12, particularly on blade edge 42 and planar bladeportion 40, is also a significant factor in controlling the temperatureat the surgical site. It has been determined that the pressure appliedto blade 12 should be light, like writing with a pencil, not heavy asmany surgeons have become used to with other bone cutting instruments.

While the irrigation is used for cooling, the coolant solution need notbe chilled. Room temperature (18° C.) fluid has been shown to beadequate to cool the surgical site during an ultrasonic cuttingoperation with blade 12. This is, of course, more convenient andfacilitates keeping extra fluid ready without concern for keeping itrefrigerated. An exemplary flow rate is approximately 100 cc/min.

Although the invention has been described in terms of particularembodiments and applications, one of ordinary skill in the art, in lightof this teaching,, can generate additional embodiments and modificationswithout departing from the spirit of or exceeding the scope of theclaimed invention. For example, blade 12 may be provided on oppositelateral surfaces with a pair of longitudinally extending recesses orgrooves (not shown) instead of through-slot 56. Each such elongaterecess or groove would communicate at an upstream end with passageway orbore 52 and would be provided at a downstream end with a circularfluid-distribution recess having an inclined surface 61 or 62.

Accordingly, it is to be understood that the drawings and descriptionsherein are proffered by way of example to facilitate comprehension ofthe invention and should not be construed to limit the scope thereof.

What is claimed is:
 1. An ultrasonic surgical blade comprising a bladebody and a shank fixed at one end to said blade body and operativelyconnectable at an opposite end to a source of ultrasonic vibrations,said blade body having a smooth continuous cutting edge including atleast one linear section, said shank being provided with a boreextending parallel to a longitudinal axis of the surgical blade for theconveyance of cooling fluid to said blade body, said blade body beingprovided with an elongate through-slot extending substantially parallelto said axis, said through-slot communicating at one end with said bore,said through-slot extending substantially parallel to said linearsection and substantially along an entire length thereof for deliveringcooling fluid to said linear section effectively along said entirelength.
 2. The surgical blade defined in claim 1 wherein said cuttingedge is disposed in a single plane and has an arcuate section.
 3. Thesurgical blade defined in claim 2 wherein said cutting edge includes apair of straight sections continuous with said arcuate section atopposite ends thereof, said linear section being one of said straightsections.
 4. The surgical blade defined in claim 3 wherein said straightsections are oriented substantially parallel to said axis and saidthrough-slot.
 5. The surgical blade defined in claim 4 wherein saidblade body is provided at an end opposite said shank with an arcuaterecess communicating with said bore and extending around saidthrough-slot at an end opposite said bore, for distributing fluid fromsaid through-slot towards said cutting edge.
 6. The surgical bladedefined in claim 2 wherein said arcuate section is substantiallycircular and is disposed on said blade body opposite said shank.
 7. Thesurgical blade defined in claim 1 wherein said blade body is provided atan end opposite said shank with an arcuate recess communicating withsaid bore and extending around said through-slot at an end opposite saidbore, for distributing fluid from said through-slot towards said cuttingedge.
 8. The surgical blade defined in claim 1 wherein said cutting edgeis the only cutting edge on said blade body.
 9. The surgical bladedefined in claim 8 wherein said cutting edge is disposed in a singleplane and has an arcuate section flanked by said linear section on oneside and another linear section on another side.
 10. The surgical bladedefined in claim 1 wherein said cutting edge is free of teeth, notches,apertures, serrations, and voids.
 11. An ultrasonic surgical bladecomprising a blade body and a shank connected at one end to said bladebody and operatively connectable at an opposite end to a source ofultrasonic vibrations, said blade body being substantially flatter thansaid shank, said blade body having a cutting edge, said shank beingprovided with a passageway or bore for the conveyance of cooling fluidto said blade body, said blade body being provided with exactly one openfluid distribution channel communicating with said passageway or borefor distributing fluid therefrom along at least one lateral surface ofsaid blade body when said blade body is disposed in tissues at asurgical site during a cutting operation, said shank having alongitudinal axis, said passageway or bore extending parallel to saidaxis, said fluid distribution channel being elongate and having a lengthdimension and a width dimension, said length dimension beingsubstantially parallel to said axis, said fluid distribution channelbeing open along the entire length dimension.
 12. The surgical bladedefined in claim 11 wherein said channel is provided at an end oppositesaid passageway or bore with at least one fluid distribution guidesurface for distributing fluid from said fluid distribution channeltowards said cutting edge.
 13. The surgical blade defined in claim 12wherein said guide surface has a shape similar to a shape of saidcutting edge.
 14. The surgical blade defined in claim 13 wherein saidcutting edge and said guide surface are circular.
 15. The surgical bladedefined in claim 11 wherein said channel is a throughslot traversingsaid blade body.
 16. An ultrasonic surgical blade comprising a bladebody and a shank fixed at one end to said blade body and operativelyconnectable at an opposite end to a source of ultrasonic vibrations,said blade body having a smooth continuous cutting edge, said shankbeing provided with a bore extending parallel to a longitudinal axis ofthe surgical blade for the conveyance of cooling fluid to said bladebody, said blade body being provided with an elongate through-slotextending substantially parallel to said axis, said through-slotcommunicating at one end with said bore, said blade body being providedat an end opposite said shank with an arcuate recess communicating withsaid bore and extending around said through-slot at an end opposite saidbore, for distributing fluid from said through-slot towards said cuttingedge.
 17. An ultrasonic surgical blade comprising a blade body and ashank fixed at one end to said blade body and operatively connectable atan opposite end to a source of ultrasonic vibrations, said blade bodyhaving a smooth continuous cutting edge, said shank being provided withexactly one bore extending parallel to a longitudinal axis of thesurgical blade for the conveyance of cooling fluid to said blade body,said blade body being provided with exactly one elongate through-slotextending parallel to said longitudinal axis and communicating at oneend with said bore for delivering cooling fluid to said cutting edge.18. The surgical blade defined in claim 17 wherein said cutting edge isdisposed in a single plane and has an arcuate section and a pair ofstraight sections continuous with said arcuate section at opposite endsthereof, said through-slot delivering cooling fluid to said arcuatesection and said straight sections.
 19. The surgical blade defined inclaim 17 wherein said blade body is provided at an end opposite saidshank with an arcuate recess communicating with said bore and extendingaround said through-slot at an end opposite said bore, for distributingfluid from said through-slot towards said cutting edge.
 20. The surgicalblade defined in claim 17 wherein said blade body is provided at an endopposite said shank with an arcuate recess communicating with said boreand extending around said through-slot at an end opposite said bore, fordistributing fluid from said slot towards said